It has just been announced that Moody's has downgraded the debt ratings of 15 major international banks and securities firms. This move could cost the banks billion of dollars in extra collateral. The US banks that fell into this group include Bank of America, Citigroup, Goldman Sachs, JPMorgan, and Morgan Stanley.

Moody’s announced earlier this year that it would review the ratings of 17 global investment banks and has already downgraded Macquarie and Nomura.

The current credit actions are part of a comprehensive review of the overall global banking system by Moody’s.

In the middle of last month, Moody’s downgraded Italian, Spanish, German and Austrian bank credit ratings. The U.S. banks with global capital markets capabilities have had an open dialogue with the ratings company, in an effort to soften the severity of the downgrades.

This afternoon’s announcement affected the long-term debt ratings of the bank-holding companies of five of the biggest U.S. banks; only Wells Fargo [WFC 32.34 -0.47 (-1.43%) ] was not on the list. Moody’s also looked at the short-term debt of the five bank-holding companies and the main bank operating subsidiaries of all except JPMorgan.

In an interview with CNBC in April, Morgan Stanley Chairman and CEO, James Gorman said the downgrade could affect about 8 percent of the firm’s derivatives contracts.

Downgrades of its senior debt could cost Morgan Stanley between $868 million and $7.2 billion in additional collateral and termination payments on derivatives contracts, according to SEC filings.